Finches add cigarette butts to their nests to ward off pests

It's the equivalent of chemical warfare in the animal kingdom.

Cigarettes aren't good for any animal's health, but leave it to nature to find some way of putting their toxic ingredients to use. A species of urban-adapted bird has apparently begun using cigarette butts to "bug bomb" their nests in order to prevent ticks from taking up residence, reports New Scientist.

Ticks pose a major health risk to fledgling urban house finches (Carpodacus mexicanus), sucking their blood and even eating their feathers. So finch parents do everything they can to keep their nests tick-free, but it's not easy. At some point, the birds must have noticed that when cigarette butts are used to pack the nest, the ticks stay away. It's remarkably innovative and adaptive behavior, even if it means having to live in a virtual ashtray.

Nicotine has known anti-parasitic properties, but researchers weren't sure if cigarette-decorated nests were actually providing protection from pests, or if there was some other explanation for the odd behavior. Constantino Macías Garcia and colleagues at the National Autonomous University of Mexico decided to find out. They conducted a study involving 32 finches, wherein tick infestations could be controlled.

For the experiment, the team added live ticks to 10 of the nests, dead ticks to another 10 and left 12 free of ticks. Sure enough, finch parents were significantly more likely to add cigarette butt fibers to their nests if they contained ticks. Furthermore, the weight of cigarette butt material added to nests was 40 percent greater on average when live ticks were involved instead of dead ones, indicating that the birds knew exactly what the butts were doing.

Macías Garcia found that there was a secondhand cost for the birds, however. Packing nests with cigarette butts isn't good for the birds either.

“The butts cause [genetic] damage to finches by interfering with cell division, which we assessed by looking at their red blood cells,” he said.

So it's a tradeoff, one that the birds make a careful calculation about. The danger that ticks pose is greater than the danger that the cigarette butts do. Then again, it might also be an example of a short-term advantage taking precedence over a long-term detriment. Hopefully the birds aren't sacrificing their future health, but researchers will need to conduct a long-term study to know exactly how living with cigarette butts ultimately impacts bird populations.